1. Department of Obstetrics and Gynecology; Sorlandet Hospital HF; Kristiansand Norway
2. Department of Global Public Health and Primary Care; University of Bergen; Bergen Norway
3. Medical Birth Registry of Norway; Norwegian Institute of Public Health; Bergen Norway
4. Department of Obstetrics and Gynecology; Haukeland University Hospital; Bergen Norway
5. Department of Clinical Medicine; University of Bergen; Bergen Norway
6. Faculty of Health Sciences; Department of Community Medicine; Research Group Epidemiology of Chronic Diseases; UiT; the Arctic University of Norway; Tromsø Norway